Binding reinforcement bars in concrete constructions is known to be a costly operation. By manual processes a wire is curled around the iron bars, and by means of a wire cutter the free ends of the wire are twisted.
Resent considerations not only related to the costs of binding the bars but also related to the working environment, has lead to the development of hand-held, portable devices for binding.
EP 0751270 shows a device for binding reinforcement bars for concrete constructions. The device operates by twisting a wire in a loop by a guide arm. A hook thereby binds the reinforcement bars together by twisting the wire loop.
U.S. Pat. No. 4,252,157 shows a device for binding reinforcement bars, comprising a differential gear for transferring torque from a motor to a binding head and a cutting device, respectively.
Both of the above mentioned documents disclose binders having jaws encircling the objects and which are adapted to guide a binding wire in a wire loop around the objects to be tied together. The binders further have twisting means for twisting the wire loop so as to tighten the wire loop around the objects and, thus, to tighten the objects together.
The existing binders generally have circular jaws for guiding the wire in circular loops. This is in contrast to the cross-sectional shape of the objects to be tied together, which objects typically form an oval shape, e.g. when binding two circular iron rods for reinforcing concrete constructions. The result of the circular shaped jaws is typically an excessive overuse of binding wire.
The existing binders further have twisting means arranged to twist the wire loop by gripping the wire loop, e.g. with a rotating hook without previous tightening of the wire in the wire loop. Thereby the tightening force of the wire loop increases as the loop is being twisted and thereby a satisfactory binding force is difficult to achieve.
Another example may be found in EP 1 484 249 which discloses a reinforcing bar machine comprising three motors: a feeding motor, a twisting motor and a sliding motor. The feeding motor forms part of a feeding mechanism and is used to feed the wire. A binding wire twisting mechanism includes the twisting motor and the sliding motor.
Other examples of known binding apparatuses are disclosed in U.S. Pat. No. 5,657,799, EP 0 731 238, EP 0 810 153, EP 0 332 532, EP 0 829 596, U.S. Pat. No. 4,362,192, EP 0 751 270, U.S. Pat. No. 4,252,157, and WO0194206.